Magnetic signal storing elements comprising a vacuum-evaporated magnetizable coatingapplied to a non-magnetic supporting member provided with an elastomeric adhesive layer



United States Patent MAGNETIC SIGNAL STORING ELEMENTS COM- PRISING AVACUUM-EVAPORATED MAGNET- IZABLE COATING APPLIED TO A NON-MAG- NETICSUPPORTING MEMBER PROVIDED WITH AN ELASTOMERIC ADHESIVE LAYER CharlesMaho, Kontich, Belgium, assignor to Gevaert Photo-Producten N.V.,Mortsel-Antwerp, Belgium, 21 Belgian company No Drawing. Filed Sept. 17,1963, Ser. No. 309,380 Claims priority, application Belgium, Sept. 18,1962,

41,967; Oct. 2, 1962, 42,005, 42,007 2 Claims. (Cl. 117-71) ABSTRACT OFTHE DISCLOSURE Magnetic signal storing elements such as rigid orflexible supports of tape, disc or drum form, provided withvacuum-evaporated magnetizable coatings of specifiediron-cobalt-chromium, iron-niekel-aluminum, or ironnickel-molybdenumalloys applied to a subbing layer of a synthetic elastomer ofbutadiene-acrylonitrile or aliphatic polyesteramide modified with adiisocyanate, for improved smoothness, tenacity and adhesion.

This invention relates to magnetic signal carriers of the kindcomprising a supporting member provided with a coating of a magnetizablematerial which is applied to said supporting member by vacuumdeposition.

It is an object of the present invention to provide on a supportingmember a magnetizable layer which combines desired magnetic propertiesfor use for instance in computers as magnetic storage element withdesired technological properties such as tenacity, smoothness and a goodadhesive power of the magnetizable coating to the supporting member.

It has been found that the above mentioned magnetic and technologicalrequirements can be fulfilled with a magnetic memory or signal carriercomprising a film deposited upon its supporting member, such as a tapeor drum surface, by a vacuum deposition process. Accordingly the presentinvention relates to such a memory or signal storing means and to amethod of making the same.

More especially it has been found that a vacuum deposited metal coatingconsisting of 64.5% of iron, 35% of cobalt and 0.5% of chromium, avacuum deposited metal coating consisting of 55% of iron, 28% of nickel,5% of cobalt and 12% of aluminum and vacuum deposited metal coatingsconsisting of from 15 to of iron, from 70 to 80% of nickel and from 2 to5% of molybdenum are well suited for use as magnetizable storage elementin electrical computers.

The deposition of said magnetizable metal coatings on a flexible orrigid supporting member may occur by vaporization in vacuum of thepreviously prepared metal alloys having the above composition. Such amethod is among others described in the UK. patent specification 874,541filed Feb. 27, 1957 by Associated Electrical Industries Ltd., England.

Since, however, the different metals have a difierent rate ofvaporization the metals are not deposited onto the supporting member inthe desired ratio therefore preference is given to simultaneous andcontinuous vacuum deposition of the pure metals from differentcrucibles, the metallisation velocity being adapted for each metal. Themetals are melted in the crucibles e.g. by electric high frequencyheating. The rate of vaporization of the metals is controlled e.g. bydetermining the power supplied for heating.

According to a preferred embodiment of the invention ingots of the puremetals are used in the metallizing step,

3,414,430 Patented Dec. 3, 1968 said ingots being gradually melted andvaporized in different crucibles. The crucibles are preferably heated bya very intense direct current (for instance 780 A.) which is conductedthrough the crucibles at a low voltage (for instance 38 v.). Thesuperposition of a high frequency voltage (e.g. 1000 c.p.s.) onto thedirect current voltage is very advantageous for obtaining a rapidvaporization, resulting in a uniform stream of metal vapor containing nocoarse metal particles. The metallizing of flexible foils or tapeaccording to this method may occur at a rate of m./min., the thicknessof the magnetizable coating then being of the order of magnitude of 200A.

The deposition of said magnetizable coatings may occur by means of knownapparatus for vacuum metallizing. Said magnetizable coatings arepreferably vacuum deposited in a vacuum less than 10 mm. Hg. Beforemetallizing, the supporting member is freed as usual from all adsorbedimpurities by conducting said supporting member successively through adirect current field of 7000 v. and an alternating-current field of15,000 v. and 1000 c.p.s.

To avoid oxidation of the vaporizing metal the air in the vacuumbell-jar is replaced before evacuation of the bell-jar by anon-oxidizing gas such as nitrogen gas, hydrogen gas or a noble gaswhereupon the bell-jar is evacuated to about 10* mm. Hg.

The crucibles wherein the metals to be deposited are melted are usuallymade of graphite, aluminum oxide, tungsten or tungsten carbide.

Advantageously the supporting member of the magnetizable coatingconsists of a nonferro-magnetic material for instance glass, mica, acopper containing material such as bronze or a plastic material such aspolyethylene terephthalate or polytetrafluoroethylene.

The supporting member may have all kinds of forms. Foils or narrowribbons and solid plates or cylinders may for instance be used assupporting member.

By using a support which withstands heat of about 1200 C., the vacuumdeposited ferro-magnetic layer can be annealed, in a strongly magneticfield to obtain a preferred axis of magnetization without risking todestroy the support.

If the ferro-magnetic layer is applied by vacuum deposition to asupporting member which does not withstand high temperatures, theferro-magnetic layer may still undergo changes in its structure by localand very short high-frequency heating.

The thickness of the magnetizable coatings varies preferably from 10 to10 A. It has been stated that a coating composed of 64.5% of iron, 35%of cobalt and 0.5% of chromium has a coercivity of 27.6 oersteds for athickness of 200 A. and 200 oersteds for a thickness of 40,000 A. Thisdifference in coercivity according to the thickness of the magnetizablelayer points to a difference in metallographic structure between verythin (100-300 A.) and thicker (10,00050,000 A.) layers.

A vacuum deposited layer of only some hundreds of A. (100-300 A.) havingone of the above mentioned compositions and a very low coercivity (=2oersteds) is suited for use as high speed magnetic switching element indigital computers. For a suitable method for preparing such element andthe application thereof we refer to Electronics June 26, 1959, pages44-45, which pages should be read in conjunction herewith.

The supporting member, especially if it is of plastic material ispreferably coated beforehand with an adhesive layer for theferro-magnetic layer to be vacuum deposited. Synthetic elastomers appearto be very well suited for being applied as adhesive layer. Among theseelastomers we may mention for instance copolymers of butadiene andacrylonitrile more especially of 55 parts of butadiene to 45 parts ofacrylonitrile marketed under the name Hycar OR 15 (trade name ofHydrocarbon Chemical and Rubber Company division of B. F. GoodrichCompany, Cleveland, Ohio, U.S.A.), further polyesters and polyesteramides modified with organic diisocyanates, such as those described inBritish patent specifications No. 580,524 filed Oct. 14, 1941 byImperial Chemical Industries and No. 585,205 filed Dec. 22, 1944 byImperial Chemical Industries and in US. Patents No. 2,422,271 filed Dec.17, 1943 by G. E. Vaala and C. E. Frank and No. 2,424,883 filed Nov. 20,1942 by B. J. Hobgood, T. A. Harper and R. I. Reynolds.

Synthetic elastomers which may advantageously be applied are elastomershaving in their molecule structure urethane, urea and amide groups suchas the elastomers known under the name Vulcaprene (trade name ofImperial Chemical Industries, Ltd., London, England) more especiallyVulcaprene AC 230 (trade name of Imperial Chemical Industries, Ltd.,London, England, for a polyester amide modified with hexamethylenediisocyanate, the polyester amide being made starting from ethyleneglycol, adipic acid and ethanol amine). This modified polyester amide isapplied from a mixture of acetone and ethyl lactate (50:50) preferablyto a polyethylene terephthalate support. The thickness of the dryadhesive layer is not critical, for instance layers of from 50 to 200 A.sufiice.

Example A poly(ethylene terephthalate) support of 25 thickness andcoated with an adhesive layer of Vulcaprene AC 230 (trade name) having athickness of 6,4 is vacuum metallized (the vacuum being 10- mm. Hg.)with a magnetizable coating of the following composition: 55% of iron,28% of nickel, of cobalt and 12% of aluminum. Each of said metals arevaporized simultaneously in separate crucibles. The thickness of thevacuum deposited coating is 3;/.. The coercivity of said coating is 26oersteds and the remanence 200 gauss.

What I claim is:

1. A magnetic signal storing element comprising a nonmagnetic supportingmember and a vacuum-evaporated magnetizable coating applied to a subbinglayer thereon, wherein said coating has a composition selected from thegroup consisting of 4 (A) 64.5% of iron, 35% of cobalt and 0.5% ofchromium (B) of iron, 28% of nickel, 5% of cobalt and 12% of aluminum,and (C) from 15 to 25% of iron, from to 80% of nickel and from 2 to 5%of molybdenum, and wherein said subbing layer consists essentially of asynthetic elastomer selected from the group consisting of a copolymer ofbutadiene and acrylonitrile and an aliphatic polyesteramide modifiedwith a diisocyanate. 2. A magnetic signal storing element according toclaim 1, wherein the non-magnetic support is polyethylene terephthalateand the elastomer is a copolymer of 55 parts of butadiene and 45 partsof acrylonitrile.

References Cited UNITED STATES PATENTS 1,968,569 7/1934 Ruder 148-21.52,027,996 1/1936 Mishina et al -124 X 2,192,744 3/1940 Howe 75-124 X2,200,491 5/1940 Cross et al. 75-170 X 2,439,983 4/1948 Morgan et al117-107 X 2,442,219 5/ 1948 Stanley 75-126 X 2,724,663 11/1955 Bond117-107 2,726,179 12/ 1955 Ortlieb et al 117-227 2,757,099 7/1956 Speedet a1 117-7 2,783,170 2/1957 Littmann 148-120 2,891,883 6/1959 Howe75-170 X 3,115,479 12/1963 Windemuth et al. 117-138.8 X 3,116,15912/1963 Fisher et al 117-71 3,149,996 9/1964 Wagner et al 117-723,247,017 4/1966 Eichler et a1 117-235 OTHER REFERENCES Williams et al.:Magnetic Domain Patterns on Thin Films, J. of Appl. Phys., 28, 5, pp.548 to 555.

WILLIAM D. MARTIN, Primary Examiner.

W. D. HERRICK, Assistant Examiner.

